(a) Field of the Invention
The present invention relates to a tube tightening structure for collapsible vehicles, more particularly to a tube tightening structure that has a handy wrench and a positioning element to prevent turning of telescopic tubular elements during length adjustment.
(b) Description of the Prior Art
Many articles are provided with a collapsible structure to enable them to be compact so as to facilitate carrying, storage, or transport. Telescopic structures are therefore commonly used, for instance, in length adjustable tubular members. One very common instance is collapsible bicycle, in which telescopic structures are provided on the longer and higher fame tubes to enable the collapsible bicycle to be very compact suitable for carrying and storage. In order to secure telescopic structures in a speedy manner, a tube tightening member having a handy wrench is often used. With reference to FIGS. 5 and 6, the end portion of an outer tube A of a telescopic tube is provided with a groove A1 along an axial direction, and is fitted with a tube tightening element C having a handy wrench C1. The annular inner side of the tube tightening element C is formed with a projecting strip C2 that extends relative to the groove A1 inside the tube. An inner tube B is formed with a punched V-shaped longitudinally oriented recessed groove B1 that corresponds to the strip C2 on the inner side of the tube tightening element C. A lower section of the recessed groove B1 is provided with an abutting post B2 that projects therefrom. By means of the above construction, the inner tube B may utilize the recessed groove B1 to slidably displace along the strip C2 on the inner side of the tube tightening element C in a telescopic manner and abut thereagainst to prevent turning. Besides, the abutting posts B2 is provided to abut against the strip C2 on the inner side of the tube tightening element C to constitute a stop function.
In the above-mentioned prior art structure, the strip on the annular inner side of the tube tightening element has to be separately formed and processed. As the construction of the tube tightening element is complicated and has a particular configuration, its adaptability is poor. Besides, since the strip abuts against the recessed groove, scratches may easily occur. Further, the abutting post on the lower section of the recessed groove is inserted into a separately formed hole, the processing of the wall of the recessed groove and the securing of the abutting post are time-consuming. Improvements thereon are therefore necessary.